As a method of reading out an image signal (image data) from an image sensor of an imaging device, a pixel addition readout method and a cutout readout method are known. In the pixel addition readout method, an image signal is read out from a plurality of pixels as a single pixel. In the cutout readout method, an image signal is read out from each pixel. Each of the readout methods has both advantages and disadvantages.
The pixel addition readout method has advantages that: an image signal can be read out with low electric power for an image of a wide-angle view; sensitivity is improved since image signals of a plurality of pixels are added and read out; and a proportion of noise contents in image signals is reduced. Disadvantages of the pixel addition readout method are, for example, that: resolution of an image is deteriorated since image signals of a plurality of pixels are added; and an image includes jaggies due to phase-shifting between pixels.
As to the cutout readout method, advantages are that: a high-resolution image can be obtained; and an image includes less jaggies. Disadvantages of the cutout readout method are that: an angle of view is narrow; and sensitivity is lower than that in the pixel addition readout method.
As described above, each of the readout methods has distinctive advantages and disadvantages, respectively. Therefore, a readout method of selecting an optimal readout method according to a zoom magnification or a subject lightness indicating brightness of a subject is employed.
For example, Patent Literature 1 discloses an imaging device that switches between the pixel addition readout method and the cutout readout method (non-pixel-addition method) according to a zoom magnification. In this imaging device, variable magnification processing and trimming processing are performed on a read-out image to fit the image to an image size for display. With this imaging device, which switches between the readout methods, an image with high resolution can be shown on a display without affecting an image displayed in an electronic viewfinder.
Moreover, Patent Literature 2 discloses an imaging device that reads out image signals by switching in each frame between a live-view readout method (cutout readout method) and the pixel addition readout method, when a subject lightness is low. In this imaging device, an image is displayed on a display during a period in which image signals are read out by the live-view readout method, while automatic focus is controlled during a period in which image signals are read out by the pixel addition readout method.
Furthermore, Patent Literature 3 discloses an imaging device that the pixel addition readout method is set when a shooting location is dark, while the cutout readout method (thinning-out readout method) is set when a shooting location is light.